1. Field of the Invention
This invention relates to a semiconductor laser device with an inner stripe structure that attains laser oscillation at an oscillation wavelength ranging from 660 nm to 890 nm.
2. Description of the Prior Art
In recent years, molecular beam epitaxy (MBE) and metal organic-chemical vapor deposition (MO-CVD) have been used as a crystal layer growth method for the production of semiconductor laser devices, especially GaAlAs semiconductor laser devices. According to these growth methods, a striped groove for the confinement of current therein that is formed on the substrate cannot be buried with a semiconductor material during a crystal growth process, but a growth layer with a uniform thickness is formed within the striped groove in accordance with the shape of the striped groove, and accordingly a built-in structure for confining current and carrier therein cannot be formed until a double-heterostructure in which an active layer is sandwiched between a pair of cladding layers has been disposed on the substrate. FIGS. 2(A) to 2(D) illustrate the above-mentioned method in which, as shown in FIG. 2(A), on an n-GaAs substrate 1, a double-heterostructure for sandwiching an n-active layer 3 between the n-cladding layer 2 and the p-cladding layer 4 is formed, and then an n-GaAs current blocking layer 5 having a conductive type different from that of the p-cladding layer 4 is formed on the p-cladding layer 4. Then, a striped groove is formed in the current blocking layer 5 by an etching technique, as shown in FIG. 2(B), in such a manner that the striped groove does not reach the p-Al.sub.0.5 Ga.sub.0.5 As cladding layer 4. If the groove reached the p-cladding layer 4 so as to expose the p-cladding layer to the outside, the exposed surface of the p-cladding layer 4 is oxidized, which makes impossible the succeeding epitaxial crystal growth thereon. Then, the wafer with the above-mentioned striped groove is fed to the growth chamber of a MBE or MO-CVD apparatus. When the wafer is subjected to a molecular beam epitaxial treatment in the growth chamber, it is heated up to a temperature of 800.degree. C. while being irradiated with As molecular beams. When the wafer undergoes a metal organic-chemical vapor deposition treatment, it is heated up to a temperature 800.degree. C. while being irradiated with AsH.sub.3 gas. By such a heating treatment, as shown in FIG. 2(C), the bottom portion of the striped groove of the current blocking layer 5 is etched so that the portion of the p-cladding layer 4 corresponding to the striped groove of the current blocking layer 5 is exposed to the outside. Then, as shown in FIG. 2(D), a p-Al.sub.0.5 Ga.sub.0.5 As layer 6 and a p-GaAs cap layer 7 are successively grown on the wafer, resulting in a semiconductor laser device in which the n-GaAs current blocking layer 5 functions to confine current and light therein.
However, the above-mentioned production process has at least two difficult problems. Firstly, in the step shown in FIG. 2(B), it is very difficult to timely cut off the etching treatment with good reproducibility to thereby leave the portion with a thin thickness of the n-GaAs current blocking layer corresponding to the bottom portion of the striped groove. Secondly, in the step shown in FIG. 2(C), when the portion of the n-GaAs current blocking layer 5 corresponding to the bottom portion of the striped groove is subjected to a heat-etching treatment, it is very difficult to remove the said portion of the current blocking layer 5 with good reproducibility without thermally damaging the p-AlGaAs cladding layer 4.